Many different compression or encoding schemes are available for compressing or encoding digital video images and other digital images. For example, the Moving Picture Experts Group (“MPEG”) encoding standards, including MPEG-1, MPEG-2, and MPEG-4, are routinely used to encode video images. As another example, the Joint Photographic Experts Group (“JPEG”) encoding standards are routinely used to encode still images. Typical encoding standards compress images by dividing an image into multiple blocks and then encoding each of the blocks separately.
Compressing video or other image data often results in a loss of information. For example, encoding schemes often use transform coefficients, such as discrete cosine transform (“DCT”) coefficients, to represent an image. Typical encoding schemes divide the transform coefficients by a quantization parameter, which often truncates higher frequency transform coefficients more than lower frequency coefficients. Also, typical encoding schemes have difficulty compressing video images when the video images contain a scene that is fading in or fading out or when two scenes are cross-fading (one scene is fading in while another scene is fading out).
These and other problems often cause noticeable flaws or distortions in images displayed after decoding. As an example, distortions around sharp edges in an image (referred to as “ringing artifacts”) and distortions along the borders of the blocks (referred to as “blocking artifacts”) may be created.